Cellulose, (C.sub.6 H.sub.10 O.sub.5).sub.n or (C.sub.6 H.sub.7 O.sub.2)(OH).sub.3 !.sub.n, is a readily available, naturally occurring polymer, comprising anhydroglucose units joined by an oxygen linkage to form long molecular chains. Modified cellulose, formed by substitution of appropriate radicals for the hydroxyl groups on the cellulose backbone, are well known. In particular, cellulose esters are widely used in applications such as coatings, pharmaceutical, and plastics. Modified cellulose material tends to be more environmentally compatible than other types of polymers, e.g., some cellulose esters have been shown to be biodegradable. See, for instance, Edgar et al., U.S. Pat. No. 5,521,304, and Buchanan et al., U.S. Pat. Nos. 5,580,911, 5,559,171, 5,446,079, and 5,292,783.
It is often desirable to protect active agents, such as cleaning agents (e.g., bleaches), medicaments, pesticides (e.g., insecticides) and herbicides, catalysts, colorants (e.g., inks and pigments) and the like, from their surrounding environment (or vice versa, i.e., to protect the environment from the active agent). For instance, it may be desirable to prevent bleaching agents from acting on fabric until the fabric is totally immersed in water, or to prevent medicaments from acting until they have reached a certain location in the body.
In particular, although the present invention is not so limited, various efforts have been made in the past to incorporate cleaning agents into a film-forming or matrix material that dissolves at an appropriate time to release the cleaning agent. Encapsulation of chlorine-containing bleaching agents with pH-sensitive coatings from non-aqueous solutions of fatty acids is described by Alterman et al. in U.S. Pat. Nos. 3,908,045, 3,944,497, 3,983,254, and 4,124,734. Likewise, Mazzola describes, in U.S. Pat. Nos. 4,078,099, 4,126,717, and 4,136,052, the use of molten fatty acid-containing coatings. Such fatty acids, oils, and waxes are unsuitable for many cleaning applications because they tend to contribute heavily to enhanced foaming and tend to leave a residue on the cleaned surface.
U.S. Pat. No. 4,762,637 (Aronson et al.) teaches the use of pH-sensitive coatings of copolymers from carboxylic acids, carboxylic anhydrides, alkyl partial esters thereof, and their salt derivatives. These materials are unsuitable for many applications, due to their tendency to persist in the environment.
U.S. Pat. No. 5,000,869 (Dittert) describes the use of so-called enteric polymers such as cellulose acetate phthalate, hydroxypropyl methylcellulose phthalate, and polyvinyl acetate phthalate for encapsulation of tetrachloroglycoluril, a bleaching and cleaning agent previously commercially available from Diamond Shamrock. These coatings are said to dissolve under mild (near-neutral), to alkaline conditions. However, phthalated enteric polymers, such as cellulose acetate phthalate, can break down to yield free phthalic acid when stored in contact with moisture. In doing so, their pH-sensitivity is diminished or lost, and in some cases, the polymer becomes totally insoluble in aqueous buffer.
Encapsulated or matrix-containing medicaments are also well-known. pH-sensitive cellulose-based polymers having pendant carboxyl groups such as cellulose acetate phthalate, cellulose acetate trimellitate, and hydroxypropyl methylcellulose phthalate are well known throughout the pharmaceutical industry as enteric polymers. They are used to encapsulate medicaments that are either destroyed on exposure to strong acid conditions found in the stomach (pH&lt;3) or to protect the stomach itself from the medicament, such as aspirin. As the coated medicament leaves the stomach and enters the small intestine, the pH increases to above about 5, whereupon the pendant carboxyl groups begin to ionize, and the coating begins to dissolve, releasing the medicament. In addition to the aforementioned problems associated with phthalated cellulose esters, however, the trimellitic moiety also tends to be unstable. Thus, neither the phthalate nor the trimellitic cellulose esters are desirable when long term storage (&gt;2 years) stability is desired.
Use of such enteric polymers as encapsulating agents for solid chlorine-containing bleach components in cleaning formulations, especially laundry detergent, is highly unsuitable because such coatings are very water-sensitive and dissolve at a relatively low pH. This means that if the coated bleach particles are packaged in direct contact with laundry detergent, the presence of incidental moisture will result in a localized increase in pH, because alkali such as sodium carbonate or sodium silicate begins to dissolve on contact with water. As the pH increases, the enteric coating begins to dissolve prematurely, exposing the bleaching agent. If the bleach particles and detergent are in contact with fabric, localized bleaching or pin holing will result.
In this regard, premature bleach release could be minimized if coatings are used for encapsulation that will only dissolve at, for instance, pH&gt;9, and not before. As more alkalinity (higher pH) is needed to dissolve the coating, greater protection of the bleach particles would be afforded by providing a strong alkaline buffering capacity; that is to say, more than incidental wetting will be needed to dissolve sufficient alkali in the detergent to raise the pH and cause the coating to dissolve. Thus the fabric will be protected from the bleach particle until a copious amount of water is present and the bleach particles are evenly dispersed in the liquid.